1. Field of the Invention
This invention relates to a method of forming holograms which allows simple and precise adjustment of the relative intensities of the object and reference beams and to apparatus for practicing that method including an electronic device for providing an indication of the relative beam intensity at the photographic media and fiber optic means for conducting light from a coherent light source to the object and photographic media and for adjusting the relative intensities of these two light paths.
2. Prior Art
In the formation of a hologram a photographic media receives an object beam of light reflected from an object surface which is illuminated with a temporarly and spatially coherent source as well as a reference beam of light directly from the source. The media records the interference patterns between these two coherent light systems. This interference pattern encodes information about the three-dimensional nature of the illuminated object surface and upon development of the photographic media and illumination with an appropriate light source, a three-dimensional image of the object surface may be reconstructed.
The quality of the reconstructed image depends, among other things, on the relative intensities of the object and reference beams reaching the photographic media during the formation of the hologram and the relative length of the light paths from the laser to the photographic media for both the reference beam and the object beam. Generally, the path lengths should be as close to equal as possible and the reference beam should have about two to three times the intensity of the object beam at the photographic media to form a good hologram, but this latter ratio may vary as a function of the object surface and the particular photographic emulsion that is employed.
In conventional holographic set-ups it is often difficult to achieve the ideal ratio of reference beam to object beam intensity, preserve the optimum ratio of reference and object beam path lengths and simultaneously achieve a geometry which properly illuminates the surface of the object on which a hologram is being formed. In conventional apparatus the laser beam is divided into object and reference beams by a beam splitter which usually takes the form of a partially silvered mirror. The beam intensity ratio is often adjusted by shifting a beam splitter whose reflectance is variable in order to modify the percentage of light diverted into the two beams. Diffusers formed of coated glass or the like are often placed in the light beam that illuminates the object to minimize specular reflection to the plate.